cc: Provide notifications when resources are available.

The DelegatedRendererLayer collects unused resources, but we'd like
the embedder to know when resources are available for it to pick up.
This adds a callback to inform the embedder when resources are
available.

Tested by new conditions in all the LayerTreeHostDelegatedTests.

R=piman
BUG=263069

Review URL: https://chromiumcodereview.appspot.com/24303008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224923 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224923
drive: Remove FileCache::IterateOnUIThread

Remove FileCache::IterateOnUIThread().
Rewrite user code (SyncClient and DebugInfoCollector).

BUG=231222
TEST=unit_tests
R=hidehiko@chromium.org

Review URL: https://codereview.chromium.org/24285005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224924 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224924